This invention relates to an improvement of the sensing coil in a hard-of-hearing aid (hereinafter referred to as "a hearing aid", when applicable).
The sensing coils in individual hearing aids worn on persons who have difficulty in hearing (hereinafter referred to as "hard-of-hearing persons", when applicable) are magnetically coupled to a signal current corresponding to voice which flows in an induction coil which is suitably laid in a room, to allow a number of hard-of-hearing person to hear the voice. A variety of induction coils and sensing coils for this purpose have been proposed in the art.
A method of hearing voices by utilizing the magnetic coupling is superior to a method of hearing voices directly through microphones in that effects of the distances between talkers and listeners and of environmental noises can be limited, the S/N ratio can be improved, and especially the former method is useful in teaching hard-of-hearing children.
However, the conventional sensing coil employed in the former method still has problems to be solved as follows: The conventional sensing coil is fixedly mounted in a predetermined positional relation to its hearing aid body, while the strength of the voice magnetic field is directional in distribution at a hearing position. Accordingly, whenever a person wearing the conventional hearing aid turns, the direction of the sensing coil is also turned, and therefore the output acoustic pressure of the hearing aid is greatly changed. This is a great obstruction in training or teaching the hard-of-hearing children, especially in the lesson of music or in the physical training which is achieved by moving their bodies.
In order to eliminate this difficulty, a variety of sensing coils have been proposed in the art; however; they are still unsatisfactory because they have dead angles.